Since the cause of breast cancer is not fully understood, there is no way to definitely prevent it. However, making healthy lifestyle choices may reduce your chance of developing the disease.
We all make trade-offs in our lifestyle against our risk of various cancers – whether it’s how much alcohol we drink, or how much time we spend in the sun. Consider how the following factors affect your risk of breast cancer, and whether you need to make lifestyle modifications to reduce your risk.
Excess weight after menopause
Women who are overweight or obese after menopause have a higher risk of developing breast cancer and those who have been treated for breast cancer have a higher risk of having a recurrence. After menopause, oestrogen is produced in fat tissue rather than in the ovaries, so women who are overweight have higher oestrogen levels compared to women of a healthy weight.
Being overweight before menopause doesn't seem to carry the same risk. However, weight gained during that time is likely to carry over into the post-menopausal setting, so it's wise at any age to keep weight within a healthy range.
To maintain a healthy weight:
- Eat plenty of vegetables, fruits, pulses and wholegrain foods
- Limit energy-dense foods (high calorie, high fat) and sugar-added food and beverages
- Limit alcohol
- Pay attention to portion sizes and reduce snacking.
It's also important to incorporate exercise into your daily routine.
You can calculate your healthy weight range here using Health Navigator's BMI calculator.
Many large studies have shown that engaging in regular physical activity can reduce your risk of developing breast cancer. It also decreases the risk of recurrence in those who have already been treated for breast cancer. Compared to women who are inactive, those who exercise for three to four hours a week can reduce their risk by 20-30%.
Exercise can range from moderately intense activities such as brisk walking to vigorous activity such as jogging, tennis, gym workouts and other aerobic exercise.
The World Health Organisation recommends that adults should do at least 150 minutes of moderate-intensity aerobic physical activity throughout the week or do at least 75 minutes of vigorous-intensity aerobic physical activity throughout the week or an equivalent combination of moderate- and vigorous-intensity activity.
Regular exercise also improves emotional well-being. It can reduce stress levels, help you sleep and enhance your quality of life. If you find it difficult to fit an exercise routine into your schedule or you lack motivation, it may help to join a class or persuade a friend to exercise with you. You can also try to incorporate extra activities into your daily life:
- Choose to walk or bike instead of driving
- Take the stairs instead of the lift
- Park further away from your destination and walk
- Go for a brisk walk or swim during your lunch break
- Using a pedometer may help you monitor your activity levels and help you to set targets.
Regular exercise helps you to maintain a healthy weight and can reduce the levels of oestrogen, insulin and insulin-like growth factors in your body. These substances all contribute to the growth of breast cancer cells.
Drinking alcohol has been firmly established as a risk factor for developing breast cancer. Alcohol changes the way the body metabolises oestrogen, causing blood oestrogen levels to rise. There is no safe level of alcohol consumption – even one drink a day will slightly increase your lifetime risk of breast cancer, and the risk increases the more you drink.
Read the Cancer Society’s position statement on Alcohol and Cancer.
Use of combined hormone replacement therapy
Results from the Million Women Study, the Women's Health Initiative Study and the Nurses Study showed that women taking combined hormone replacement therapy, using both oestrogen and progestogen, had an increased breast cancer risk during use and for two to five years afterwards. The longer you use it for, the higher your risk. Oestrogen-only HRT(prescribed for women who no longer have a uterus) is associated with little or no change in breast cancer risk.
If you are considering using HRT to control severe menopausal symptoms, talk to your doctor about the risks versus benefits. It is recommended that HRT use should be at the lowest possible dose to control symptoms, for the shortest possible time.
Oral contraceptive pill and Depo Provera use
The risk of developing breast cancer in women who currently or recently used contemporary, combined (oestrogen and progestogen) oral contraceptive pills is higher than in women who have never used hormonal contraceptives. The risk increases with longer duration of use. However the absolute increase in risk is quite small. The increase in risk also applies to the use of hormone secreting intra-uterine devices
Oral contraceptive use is considered relatively safe for women under the age of 40 who are not already at high risk of breast cancer, and it reduces the risk of ovarian and endometrial cancers.
Depo Provera, an injectable progesterone, has been shown to slightly increase breast cancer risk but the increase in risk disappears after discontinuation of use.
Timing of childbearing – age at first birth, number of children and breastfeeding
Not having children or having your first child over the age of 30 increases your risk of breast cancer because of the continuous exposure to oestrogen during menstrual cycles. Having children at a younger age and having multiple children reduces the risk, as does breastfeeding, especially if you breastfeed continuously for at least a year. These factors are most strongly associated with the risk of oestrogen receptor positive breast cancer. The risk of triple negative breast cancer is reduced by breastfeeding but doesn't seem to be reduced by early age at first birth.
Although childbirth lowers your lifetime risk of breast cancer, it's important to know there is a short-term increase in risk for two to five years after giving birth. It's not something to stress about – breast cancer is less common in younger women – but it does mean you should take breast lumps or other changes after childbirth seriously, and insist on being referred for assessment if you're concerned.
Disrupted sleep patterns
Disruption of circadian rhythms (sleep patterns) has been linked to development of breast cancer in women – underlying causes could be increased exposure to hormonal alteration, or changes in immune system and biological processes. Circadian disruption is usually caused by shift work, short sleep duration and exposure to light at night.
Breast cancer in flight attendants
There have been several conflicting studies about the risk of breast cancer among air crew. Most recently, a 2016 meta-analysis concluded that the incidence of breast cancer among female flight attendants is 40% higher than in the general population – statistically, that’s considered a moderately higher incidence1. There’s no definitive evidence as to the cause, but studies suggest it’s due to occupational exposure to risk factors, mainly cosmic radiation and disruptive sleep patterns (circadian disruption).
The meta-analysis found the dose of occupational exposure to cosmic radiation for flight attendants was twice that for the general population, though still within allowed safe levels.
Breast cancer in shift workers
In 2007, the WHO International Agency for Research on Cancer (IARC) classified shift work that involves circadian disruption as probably carcinogenic to humans based on limited evidence. A 2016 updated meta-analysis found that overall, there is a tendency towards increased risk of breast cancer either after more than 20 years of night shift, or after shorter periods with many consecutive shifts2.
- The incidence of breast cancer among female flight attendants: an updated meta-analysis Journal of Travel Medicine, November 2016, https://doi.org/10.1093/jtm/taw055
- Night Shift Work and Risk of Breast Cancer Curr Environ Health Rep. 2017 Sep;4(3):325-339. doi: 10.1007/s40572-017-0155-y.